Using or 'Edit - select' you change into object selection mode. To edit (e.g. erase or move) objects they have to be selected first. Selected objects are highlighted in blue colour. Click on unselected objects to add them to the selection. Click on selected objects to remove them from the selection.
or 'Edit - select window' (de)selects every object in a rectangular area.
Right clicking on an object opens a property dialogue. The previously selected objects have no influence on this operation. Right clicking deselects all previously selected objects and aborts pending operations.
Using or 'Edit - properties' you get an object specific dialogue showing the properties. The meaning of this properties is explained in the documentation of the objects itself. If multiple objects of one kind are selected meaningful properties are applied to all of them. E.g. for nodes these are support conditions and nodal forces, but not the label and the coordinates. If the selection contains multiple kind of objects a dialogue is displayed for every kind of object.
You can move around objects using or 'Edit - move'. Select to points defining the displacement vector.
or 'Edit - delete' is used to delete the selected objects. Caution: Selecting a node deletes every element using this node as start or end point.